In recent years, mobile devices using various types of information have become popular, and the importance of a nonvolatile memory device such as a flash memory has increased. The nonvolatile memory device which is to be a future mainstream is required to have features such as large capacity, high speed and inexpensiveness, and representative candidates for such a memory are FeRAM, MRAM and the like. Among these devices, a phase change memory device which is one of nonvolatile memories utilizing structure change of phase change material has been studied and developed as a promising technique. In the phase change memory device, heat is applied to chalcogenide-based phase change material (germanium, antimony and tellurium) so as to change between a high-resistance amorphous state and a low-resistance crystalline state, and thereby realizing the nonvolatile memory device in which data is rewritably stored. When data is written to the phase change memory device, current caused by applying a predetermined pulse flows therein and thereby Joule heat is generated so that temperature of the phase change material is changed. By appropriately controlling the current level and pulse application time, it is possible to freely change between the amorphous state and the crystalline state. Generally, the write time for the phase change memory device requires from several tens to hundred ns.
For the purpose of realizing a high-integrated phase change memory device, a phase change memory device employing a cross point memory cell array system is proposed, in which memory cells are arranged at cross points of word lines and bit lines. Such a cross point memory cell array system is disclosed in Patent documents 1 and 2, for example. As described therein, in order to obtain sufficient current when writing data, a configuration is employed in which bipolar transistors or diode devices are used in memory cells, substituting for select transistors. Generally, when memory cells are formed using bipolar transistors, it is possible to reliably obtain the current for generating the Joule heat required for writing data.    Patent Document 1: U.S. Pat. No. 6,590,807 B2    Patent Document 2: U.S. Pat. No. 6,567,296 B1